Characterization of Monoamine Oxidases in Mesenchymal Stem Cells: Role in Hydrogen Peroxide Generation and Serotonin-Dependent Apoptosis

Application of Synephrine to Grape Increases Anthocyanin via Production of Hydrogen Peroxide, Not Phytohormones

Global warming has caused such problems as the poor coloration of grape skin and the decreased production of high-quality berries. We investigated the effect of synephrine (Syn) on anthocyanin accumulation. Anthocyanin accumulation in cultured grape cells treated with Syn at concentrations of 1 mM or higher showed no significant difference, indicating that the accumulation was concentration-independent. On the other hand, anthocyanin accumulation was dependent on the compound used for treatment. The sugar/acid ratio of the juice from berries treated with Syn did not differ from the control. The expression of anthocyanin-biosynthesis-related genes, but not phytohormones, was increased by the treatment with Syn at 24 h or later. The Syn treatment of cultured cells increased SOD3 expression and hydrogen peroxide (H2O2) production from 3 to 24 h after treatment. Subsequently, the expression of CAT and APX6 encoding H2O2-scavenging enzymes was also increased. Treatment of cultured cells with Syn and H2O2 increased the expression of the H2O2-responsive gene Chit4 and the anthocyanin-biosynthesis-related genes mybA1 and UFGT 4 days after the treatment and increased anthocyanin accumulation 7 days after the treatment. On the other hand, the treatment of berries with Syn and H2O2 increased anthocyanin accumulation after 9 days. These results suggest that Syn increases anthocyanin accumulation through H2O2 production without changing phytohormone biosynthesis. Syn is expected to improve grape skin coloration and contribute to high-quality berry production.

Cellular senescence induction leads to progressive cell death via the INK4a-RB pathway in naked mole-rats

Naked mole-rats (NMRs) have exceptional longevity and are resistant to age-related physiological decline and diseases. Given the role of cellular senescence in aging, we postulated that NMRs possess unidentified species-specific mechanisms to prevent senescent cell accumulation. Here, we show that upon induction of cellular senescence, NMR fibroblasts underwent delayed and progressive cell death that required activation of the INK4a-retinoblastoma protein (RB) pathway (termed "INK4a-RB cell death"), a phenomenon not observed in mouse fibroblasts. Naked mole-rat fibroblasts uniquely accumulated serotonin and were inherently vulnerable to hydrogen peroxide (H2 O2 ). After activation of the INK4a-RB pathway, NMR fibroblasts increased monoamine oxidase levels, leading to serotonin oxidization and H2 O2 production, which resulted in increased intracellular oxidative damage and cell death activation. In the NMR lung, induction of cellular senescence caused delayed, progressive cell death mediated by monoamine oxidase activation, thereby preventing senescent cell accumulation, consistent with in vitro results. The present findings indicate that INK4a-RB cell death likely functions as a natural senolytic mechanism in NMRs, providing an evolutionary rationale for senescent cell removal as a strategy to resist aging.

Assay of MAO Inhibition by Chromatographic Techniques (HPLC/HPLC-MS)

Monoamine oxidase (MAO) enzymes (MAO A and B) catalyze the oxidative deamination of biogenic amines, neurotransmitters, and xenobiotic amines and contribute to the regulation of the content of these active substances in mammalian organisms. The oxidation of biogenic amines by MAO produces hydrogen peroxide (H₂O₂) and aldehydes that represent risk factors for oxidative injury. The inhibitors of MAO are useful as antidepressants and neuroprotective agents. Usually, the assays of MAO determine amine deamination products or measure the H₂O₂ released by using direct spectrophotometric or fluorimetric methods. Direct methods are more prone to interferences and can afford inaccurate results. Those limitations can be avoided by using chromatographic techniques. This work describes a chromatographic method to assay MAO A and MAO B activity by using kynuramine as a nonselective substrate and the subsequent analysis of 4-hydroxyquinoline by RP-HPLC-DAD-fluorescence and mass spectrometry (MS). Alternatively, the assay uses the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin as a substrate of MAO that is oxidized (bioactivated) to neurotoxic pyridinium cations which are analyzed by HPLC. These methods are applied to assess the inhibition of MAO by bioactive β-carboline alkaloids occurring in foods, plants, and biological systems.

Circulating serotonin levels in COPD patients: a pilot study

Background

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem. Serotonin is a neurotransmitter that participates in several pulmonary functions and it has been involved in oxidative stress, which plays essential roles in the pathogenesis of COPD. The current study aimed at establishing the levels of circulating serotonin in COPD, and investigating eventual relations between serotonin and oxidative stress markers.

Methods

Whole blood serotonin was assessed in 43 consecutive patients with stable COPD and in 43 age and sex-matched healthy controls.

Results

Serotonin blood levels were significantly higher in COPD patients than in controls (median 0.81 μmol/L, IQR: 0.61–4.02 vs 0.65 μmol/L, IQR: 0.53–1.39, p = 0.02). The univariate logistic regression analysis evidenced that serotonin levels are independently associated with presence of COPD (crude OR = 7.29, 95% CI: 1.296–41.05, p = 0.003) and such an association was confirmed also after adjusting for several confounders (OR 21.92, 95% CI 2.02–237.83; p = 0.011).

Conclusions

Our study showed higher levels of circulating serotonin in COPD and an inverse correlation with the worsening of airway obstruction. Future studies are necessary to investigate the clinical utility of this finding.

Monoamine oxidase-A is a novel driver of stress-induced premature senescence through inhibition of parkin-mediated mitophagy

Cellular senescence, the irreversible cell cycle arrest observed in somatic cells, is an important driver of age‐associated diseases. Mitochondria have been implicated in the process of senescence, primarily because they are both sources and targets of reactive oxygen species (ROS). In the heart, oxidative stress contributes to pathological cardiac ageing, but the mechanisms underlying ROS production are still not completely understood. The mitochondrial enzyme monoamine oxidase‐A (MAO‐A) is a relevant source of ROS in the heart through the formation of H₂O₂ derived from the degradation of its main substrates, norepinephrine (NE) and serotonin. However, the potential link between MAO‐A and senescence has not been previously investigated. Using cardiomyoblasts and primary cardiomyocytes, we demonstrate that chronic MAO‐A activation mediated by synthetic (tyramine) and physiological (NE) substrates induces ROS‐dependent DNA damage response, activation of cyclin‐dependent kinase inhibitors p21^cip, p16^ink4a, and p15^ink4b and typical features of senescence such as cell flattening and SA‐β‐gal activity. Moreover, we observe that ROS produced by MAO‐A lead to the accumulation of p53 in the cytosol where it inhibits parkin, an important regulator of mitophagy, resulting in mitochondrial dysfunction. Additionally, we show that the mTOR kinase contributes to mitophagy dysfunction by enhancing p53 cytoplasmic accumulation. Importantly, restoration of mitophagy, either by overexpression of parkin or inhibition of mTOR, prevents mitochondrial dysfunction and induction of senescence. Altogether, our data demonstrate a novel link between MAO‐A and senescence in cardiomyocytes and provides mechanistic insights into the potential role of MAO‐dependent oxidative stress in age‐related pathologies.

Increased coiling frequency linked to apoptosis in the brain and altered thyroid signaling in zebrafish embryos (Danio rerio) exposed to the PBDE metabolite 6-OH-BDE-47

Polybrominated diphenyl ethers (PBDEs) are a group of brominated flame retardants that are ubiquitously detected in the environment and associated with adverse health outcomes. 6-OH-BDE-47 is a metabolite of the flame retardant, 2,2',4,4'-Tetrabromodiphenyl ether (BDE-47), and there is increasing concern regarding its developmental neurotoxicity and endocrine disrupting properties. In this study, we report that early life exposure in zebrafish (Danio rerio) embryos to 6-OH-BDE-47 (50 and 100 nM) resulted in higher coiling frequency and significantly increased apoptotic cells in the brain. These effects were partially rescued by overexpression of thyroid hormone receptor β (THRβ) mRNA. Moreover, exposure to 100 nM 6-OH-BDE-47 significantly reduced the number of hypothalamic 5-hydroxytryptamine (5-HT, serotonin)-immunoreactive (5-HT-ir) neurons and the mRNA expression of tryptophan hydroxylase 2 (TPH2). These results indicate that 6-OH-BDE-47 affected thyroid hormone regulation through THRβ and negatively impacted the nervous system, in turn, affecting coiling behavior. Correlations of these endpoints suggest that coiling frequency could be used as an indicator of neurotoxicity in embryos.

Inhibition of mircoRNA-34a Enhances Survival of Human Bone Marrow Mesenchymal Stromal/Stem Cells Under Oxidative Stress

BACKGROUND Mesenchymal stromal/stem cells (MSCs) are broadly used for many diseases, but the efficacy of MSC engraftment is very low due to low viability and high cell death rate under a stressful microenvironment. The present study aimed to investigate whether microRNA-34a (miR-34a), which is a downstream target of P53, is involved in H2O2-induced MSC cell death. MATERIAL AND METHODS Human bone marrow MSCs (hMSCs) were purchased from Lonza and were cultured as previously described. hMSCs were transfected with miR-34a inhibitor and exposed to H2O2. Cell proliferation assay was used to assess the survival rate of hMSCs. Real-time PCR and Western blot analysis were used to examine proliferation and survival ability of hMSCs. RESULTS H2O2 exposure significantly increased miR-34a expression in human bone marrow MSCs. H2O2 challenge induced massive MSC cell death along with reduction of expression of proliferation marker Ki67 and survival-related genes Bcl-2 and Survivin. Transfection of miR-34a inhibitor anti-34a led to a significant protective effect and rescued MSC cell death triggered by H2O2 exposure by 50%. Moreover, anti-34a dramatically increased Bcl-2 and Ki67 mRNA expression levels by over 10-fold compared to the mock control group under H2O2 exposure. The protein levels of Bcl-2 and Survivin were also rescued by anti-34a treatment by 50%. CONCLUSIONS Our results suggest that miR-34a plays a key role in oxidative stress-induced MSC cell death, and targeting miR-34a might be a promising strategy to enhance the survival rate of engrafted stem cells, which may improve therapeutic outcome.

Propranolol and Mesenchymal Stromal Cells Combine to Treat Traumatic Brain Injury

More than 6.5 million patients are burdened by the physical, cognitive, and psychosocial deficits associated with traumatic brain injury (TBI) in the U.S. Despite extensive efforts to develop neuroprotective therapies for this devastating disorder, there have been no successful outcomes in human clinical trials to date. Retrospective studies have shown that β-adrenergic receptor blockers, specifically propranolol, significantly decrease mortality of TBI through mechanisms not yet fully elucidated but are thought to counterbalance a hyperadrenergic state resulting from a TBI. Conversely, cellular therapies have been shown to improve long-term behavior following TBI, likely by reducing inflammation. Given the nonredundancy in their therapeutic mechanisms, we hypothesized that a combination of acute propranolol followed by mesenchymal stem cells (MSCs) isolated from human bone marrow would have additive effects in treating a rodent model of TBI. We have found that the treatments are well-tolerated individually and in combination with no adverse events. MSCs decrease BBB permeability at 96 hours after injury, inhibit a significant accumulation of activated microglia/macrophage in the thalamic region of the brain both short and long term, and enhance neurogenesis short term. Propranolol decreases edema and reduces the number of fully activated microglia at 7 days and the number of semiactivated microglia at 120 days. Combinatory treatment improved cognitive and memory functions 120 days following TBI. Therefore, the results here suggest a new, efficacious sequential treatment for TBI may be achieved using the β-blocker propranolol followed by MSC treatment.

SIGNIFICANCE

Despite continuous efforts, traumatic brain injury (TBI) remains the leading cause of death and disability worldwide in patients under the age of 44. In this study, an animal model of moderate-severe TBI was treated with an acute dose of propranolol followed by a delayed dose of human mesenchymal stem cells (MSCs), resulting in improved short- and long-term measurements. These results have direct translational application. They reinforce the inevitable clinical trial of MSCs to treat TBI by demonstrating, among other benefits, a notable decrease in chronic neuroinflammation. More importantly, these results demonstrate that MSCs and propranolol, which is increasingly being used clinically for TBI, are compatible treatments that improve overall outcome.

Fluoxetine treatment of rat neonates significantly reduces oxidative stress in the hippocampus and in behavioral indicators of anxiety later in postnatal life

The brain, more than any other organ in the body, is vulnerable to oxidative stress damage, owing to its requirement for high levels of oxygenation. This is needed to fulfill its metabolic needs in the face of relatively low levels of protective antioxidants. Recent studies have suggested that oxidative stress is directly involved in the etiology of both eating and anxiety behavior. The aim of this study was to evaluate the effect of fluoxetine-inhibited serotonin reuptake in nursing rat neonates on behavior and on oxidative stress in the hypothalamus and the hippocampus; brain areas responsible for behavior related to food and anxiety, respectively. The results show that increased serotonin levels during a critical period of development do not induce significant differences in food-related behavior (intake and satiety), but do result in a in a significant decrease in anxiety. Measurements of oxidative stress showed a significant reduction of lipid peroxidation in the hippocampus (57%). In the hypothalamus, antioxidant enzymes were unchanged, but in the hippocampus, the activity of catalase and glutathione-S-transferase was increased (80% and 85% respectively). This suggests that protecting neural cells from oxidative stress during brain development contributes to the anxiolytic effects of serotonin.

Monoamine oxidases in development

Monoamine oxidases (MAOs) are flavoproteins of the outer mitochondrial membrane that catalyze the oxidative deamination of biogenic and xenobiotic amines. In mammals there are two isoforms (MAO-A and MAO-B) that can be distinguished on the basis of their substrate specificity and their sensitivity towards specific inhibitors. Both isoforms are expressed in most tissues, but their expression in the central nervous system and their ability to metabolize monoaminergic neurotransmitters have focused MAO research on the functionality of the mature brain. MAO activities have been related to neurodegenerative diseases as well as to neurological and psychiatric disorders. More recently evidence has been accumulating indicating that MAO isoforms are expressed not only in adult mammals, but also before birth, and that defective MAO expression induces developmental abnormalities in particular of the brain. This review is aimed at summarizing and critically evaluating the new findings on the developmental functions of MAO isoforms during embryogenesis.

The involvement of serotonin metabolism in cigarette smoke-induced oxidative stress in rat lung in vivo

Recently, we have reported the dysregulation of circulating serotonin (5-hydroxytryptamine, 5-HT) homeostasis in patients with chronic obstructive pulmonary disease (COPD). An increase in metabolism of 5-HT has been reported to induce oxidative stress via monoamine oxidase (MAO)-dependent pathway. The present study aimed at investigating the effect of cigarette smoke exposure on the systemic circulation and local airway 5-HT levels as well as MAO-mediated oxidative pathway using a cigarette smoke-exposed rat model. Male Sprague-Dawley rats (150-200 g) were exposed to either sham air or 4% (v/v, smoke/air) cigarette smoke for 1 hour daily for 56 consecutive days. Sera, bronchoalveolar larvage (BAL) and lung tissues were collected 24 hours after the last exposure. We found a significant reduction in the reduced glutathione (rGSH) and an elevation in advanced oxidation protein products (AOPP), a protein oxidation marker, in the lung of cigarette smoke-exposed group (p < 0.05). A significant increase in 5-HT was found in serum (p < 0.05), but not in the BAL or lung, after cigarette smoke exposure. MAO-A activity was significantly elevated in the lung of cigarette smoke-exposed group (p < 0.05). Furthermore, increased superoxide anion levels were found in lung homogenates of cigarette smoke-exposed rats after incubation with 5-HT (p < 0.05), which was positively associated with the increase in MAO-A activity (r = 0.639, p < 0.05). Our findings supported the presence of GSH disruption and protein oxidation in the lung after cigarette smoke exposure. The metabolism of 5-HT by MAO-A in the lung enhanced cigarette smoke-induced superoxides, which might contribute to the pathogenesis of COPD.

Molecular Insights into Human Monoamine Oxidase B Inhibition by the Glitazone Anti-Diabetes Drugs

The widely employed anti-diabetic drug pioglitazone (Actos) is shown to be a specific and reversible inhibitor of human monoamine oxidase B (MAO B). The crystal structure of the enzyme-inhibitor complex shows the R-enantiomer is bound with the thiazolidinedione ring near the flavin. The molecule occupies both substrate and entrance cavities of the active site establishing non-covalent interactions with the surrounding amino acids. These binding properties differentiate pioglitazone from the clinically used MAO inhibitors, which act through covalent inhibition mechanisms and do not exhibit a high degree of MAO A versus B selectivity. Rosiglitazone (Avandia) and troglitazone, other members of the glitazone class, are less selective in that they are weaker inhibitors of both MAO A and MAO B These results suggest that pioglitazone may have utility as a "re-purposed" neuro-protectant drug in retarding the progression of disease in Parkinson's patients. They also provide new insights for the development of reversible isoenzyme-specific MAO inhibitors.

Alterations in striatal oxidative stress level produced by pharmacological manipulation of dopamine as shown by a novel synthetic marker molecule

Oxidative stress (OS) is thought to participate in neurodegenerative diseases such as Parkinson's disease, but the contribution of dopamine metabolism and auto-oxidation to OS in Parkinson's and other diseases is not clear. Oxidative stress in rat striatum was measured by microdialysis using a novel synthetic compound composed of tyrosine and linoleic acid (LT), and determination of the oxidation products LT-OOH and LT-epoxy by HPLC-MS. Since LT is non-diffusible through the microdialysis membrane, the oxidized products formed in microdialyzate reflect oxidation state in the extracellular compartment. The extracellular oxidative stress (OS(ec)) was compared with intracellular oxidative stress (OS(ic)) as measured by tissue levels of oxidized and reduced glutathione and 7-ketocholesterol. Reserpinization caused an increase in OS(ic) but a reduction in OS(ec). Inhibition of both subtypes of monoamine oxidase (MAO-A and MAO-B) with tranylcypromine caused a reduction in both OS(ic) and OS(ec) whereas selective inhibition of MAO-A with clorgyline caused a reduction in Os(ic) but no change in OS(ec). A high dose (10 mg/kg) of amphetamine caused an increase in OS(ec) whereas a smaller dose (4 mg/kg) caused a reduction in OS(ec). Both doses of amphetamine reduced OS(ic). The present findings are consistent with a role of monoamine oxidase as well as dopamine auto-oxidation in production of striatal OS.